Pyright can't tell what's required when mixing **kwargs: Unpack with partial

[erictraut]

Discussed in #9180

^{Originally posted by naddeoa October 8, 2024}
When you use Unpack to define the kwargs of a function (fn below) then pyright loses the ability to tell which args are actually required or not after you also use partial on that function. I'm not even sure if this a pyright issue or a typeshed issue. In general, things kind of get weird depending on the pyright version when you start using Unpack.

from functools import partial
from typing import List, TypedDict
from typing_extensions import NotRequired, Unpack


class Foo(TypedDict):
    c: List[str]
    a: int
    b: NotRequired[str]


def fn(**kwargs: Unpack[Foo]) -> None:
    print(f"a: {kwargs['a']}, b: {kwargs.get( 'b' )}, c: {kwargs['c']}")


def hardcoded(c: List[str], a: int, b: str) -> None:
    print(f"a: {a}, b: {b}, c: {c}")


fn2 = partial(fn, c=["a", "b"], a=2)
hardcoded2 = partial(hardcoded, c=["a", "b"], a=2)


fn2(b="2")  # BUG pyright says that a/c are missing in fn2
hardcoded2(b="2")
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